The oxygen levels of water discharged from hydraulic turbines used in hydroelectric installations have been known to provide an environmental problem due to the discharged water having relatively low levels of dissolved oxygen. The problem is more predominant in the summer months. During the summer months, thermal stratification of water in an upstream water reservoir creates warmer water near the surface having relatively high dissolved oxygen and colder water near the bottom of the reservoir having relatively lower dissolved oxygen. Because the water utilized by the turbines is usually taken from the bottom of the reservoir, this water presents a potentially environmental hazard when discharged downstream by the turbines.
In the building of new hydroelectric installations and the refurbishing of existing hydroelectric installations, there is an opportunity to improve the level of dissolved oxygen in the water by introducing oxygen to the water as it passes through the turbine. It is known to admit air through one or more runner blades in the turbine as disclosed in U.S. Pat. No. 5,879,130 issued Mar. 9, 1999; U.S. Pat. No. 5,896,657 issued Apr. 27, 1999; U.S. Pat. No. 5,924,842 issued Jul. 20, 1999; U.S. Pat. No. 6,155,783 issued Dec. 5, 2000; U.S. Pat. No. 6,247,893 issued Jun. 19, 2001, and U.S. Pat. No. 6,454,533 issued Sep. 24, 2002. However, each of these turbines requires introducing air through at least one of the moveable turbine runner blades. This requires complex blade manufacture and the introduction of air through a moving part.
It is also known from U.S. Pat. No. 5,941,682 issued Aug. 24, 1999 to enhance oxygen content in water passed through a turbine by having a gas chamber substantially surrounding an upper peripheral portion of the draft tube and by having a continuous gas discharge slot that extends about an entire circumference of the water passage. Gas is discharged from the slot under pressure into the water passage so that the level of dissolved oxygen in the water discharged from the turbine is increased. To utilise this arrangement in existing turbine installations, however, involves costly removal of an upper portion of the draft tube along with a 360° surrounding portion of the concrete from the foundation.
It is also known from U.S. Pat. No. 4,142,825 issued Mar. 6, 1979; U.S. Pat. No. 4,142,826 issued Mar. 6, 1979; and U.S. Pat. No. 4,146,351 issued Mar. 27, 1979, to admit air through the foundation of the draft tube. The purpose of this air admission however, is to quiet pressure pulsations and cavitation problems caused by high or part load rope vortices within the draft tube. A finite number of shroud covered air outlets extend through the draft tube to provide limited air admission. These patents, however are not concerned with increasing dissolved oxygen in the water passing through the turbine which requires a greater amount of air admission into the working fluid. U.S. Pat. No. 4,142,825 discloses an air eductor having a flow control plate overlying an air box. The air box has front upstream and downstream plates providing a convergent-divergent flow path with the cover plate. A series of small air holes are located spaced along the downstream plate at the throat adjacent the juncture of the convergent-divergent plates for introducing a limited amount of air into the working fluid for the purpose of stabilizing turbine operation by making this operation smoother, quieter and more reliable during part load conditions. Admission of the air through the air holes is accomplished by a venturi or suction like effect as fluid passes over the convergent-divergent plates. The amount of air introduced into the working fluid is limited, because once the amount of air starts to rise, it can adversely effect the flow of the working fluid and result in decreased efficiency of operation.
Accordingly, there is a need for an improved deflector that introduces sufficient amounts of oxygen into the water passing through the turbine for the purpose of increasing the dissolved oxygen content in water discharged from the turbine.